1. Field of the Invention
The present invention relates to a radio transmission method and a radio transmission apparatus which are suitable for transmitting radio signals between various devices to construct a local area network (LAN).
2. Description of the Related Art
A method has been proposed for constructing a radio network wherein the number of communication stations is fixed, e.g. four stations. The network system transmits information using a frame structure. A portion of the frame is allocated as a management information transmission region, wherein information necessary for operating the network is transmitted. Further, a radio transmission frame has been proposed that has a station synchronizing section in the management information transmission region to identify the communication stations in the network (U.S. patent application Ser. No. 09/252,807). By utilizing such a frame structure in a star-type transmission network managed by a central control station, it is possible to construct a network that conducts net-type information transmission.
FIG. 13 shows an example of structure for a radio transmission frame according to the conventional method. In FIG. 13, a transmission frame is defined having a constant transmission frame period 135. A management information transmission region 136 and an information transmission region 137 make up each frame period 135. DLM 131 (Down Link Management) is a down link management information transmission section 138 for frame synchronization at the beginning of the frame. ULM 132 (Up Link Management) is a station synchronous transmission section 139 that directly follows DLM 131. DLM 131 is a down link management region (frame synchronous area) that includes frame synchronous information and ULM 132 is a station synchronous section (node synchronous area).
The station synchronous transmission section 139 respectively allocates a section to each communication station in the network. This sectioned structure prevents signals from a plurality of communication stations from colliding into each other. By using this sectioned structure, a network station can identify the linking state between all of the communication stations in the network simply by receiving all signals except those sent by itself. Further, by reporting this linking state information to each other in the station synchronous transmission section 139 of the next frame, the other communication stations can grasp the linking state of the network.
As shown in FIG. 13, this conventional method, has the maximum number of communications stations in the station synchronous transmission section 139 set to four, thus the length of the ULM is fixed.
That portion of the frame outside the management information transmission region 136 is the information transmission region 137. An isochronous transmission section 140 is located in the first portion of the information transmission region, next to the management information transmission region, as a first information transmission region 133. An asynchronous transmission section 141 is located in the remaining portion as a second information transmission region 134.
In the above-described conventional radio network, there is a problem that when a network is constructed having more fixed stations than actual communication stations, some of the allocated sections are not used. Because the number of sections is fixed, this means that some space in the fixed transmission frame is wasted, even if this limits the information that can be transmitted in the information transmission region 137 of the frame. In addition, any unused sections in the ULM take away from the space which could be used by the asynchronous transmission section 141.
However, this problem cannot be fixed simply by making the number of stations variable. For example, when the information transmission region is disposed next to the management information transmission region, if the length of the management information transmission region is variable based upon the number of communication stations in the network, then the starting position of the information transmission region is shifted. This causes another problem if a communication station relating to this transmission does not notice that the starting position of the information transmission region within the frame has changed, then information in the isochronous transmission section can be lost.